Method for transmitting a paging message and device supporting the same

ABSTRACT

A method for a wireless device in a wireless communication system includes receiving a paging from a distribution unit (DU) of a base station; and upon receiving the paging message, initiating a service request procedure. Further, the paging is based on paging information transmitted from a central unit (CU) of the base station to the DU of the base station. The paging information includes paging discontinuous reception (DRX) information and paging priority information. The DU of the base station has a radio link control (RLC) layer, a media access control (MAC) layer and a physical layer of the base station. In addition, the CU of the base station has a radio resource control (RRC) layer, a service data adaptation protocol (SDAP) layer, and a packet data convergence protocol (PDCP) layer of the base station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of co-pending U.S. patent applicationSer. No. 15/951,936 filed on Apr. 12, 2018, which claims the prioritybenefit under 35 U.S.C. § 119(e) to U.S. Provisional Application Nos.62/533,135 filed on Jul. 17, 2017 and 62/484,901 filed on Apr. 13, 2017,all of which are hereby expressly incorporated by reference into thepresent application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method in which a distributed unit (DU) of abase station (BS) transmits a paging message to a user equipment (UE),and a device supporting the same.

Discussion of the Related Art

Efforts have been made to develop an improved 5^(th)-generation (5G)communication system or a pre-5G communication system in order tosatisfy a growing demand on radio data traffic after commercializationof a 4^(th)-generation (4G) communication system. A standardization actfor a 5G mobile communication standard work has been formally started in3GPP, and there is ongoing discussion in a standardization working groupunder a tentative name of a new radio access (NR).

Meanwhile, an upper layer protocol defines a protocol state toconsistently manage an operational state of a user equipment (UE), andindicates a function and procedure of the UE in detail. In thediscussion on the NR standardization, an RRC state is discussed suchthat an RRC_CONNECTED state and an RRC_IDLE state are basically defined,and an RRC_INACTIVE state is additionally introduced.

Meanwhile, the base station (e.g., gNB) of NR may be divided into acentral unit and a distributed unit. That is, the gNBs can behierarchically separated and operated. The central unit may perform thefunctions of the upper layers of the base station, and the distributedunit may perform the functions of the lower layers of the base station.Because the Paging message received from the Core Network (CN) can beinterpreted at the RRC layer in the CU but transmission of the paging ispossible in the DU through the radio, the signaling between the CU andthe DU is necessary.

SUMMARY OF THE INVENTION

According to a prior art, there is no procedure for performing thepaging in case of CU-DU split.

According to one embodiment of the present invention, a method fortransmitting a paging message in a wireless communication systemincludes: receiving a paging information from a Central Unit (CU) of thebase station; and transmitting the paging message based on the paginginformation to a User Equipment (UE), wherein the DU is a lower layer ofthe base station, and the CU is a higher layer of the base station.

The CU includes a radio resource control (RRC) layer and a packet dataconvergence protocol (PDCP) layer of the base station, and wherein theDU includes a radio link control (RLC) layer, a medium access control(MAC) layer and a physical (PHY) layer of the base station.

The paging information may include at least one of UE Identity IndexValue, UE Paging Identity, Paging Discontinuous Reception (DRX), List oftracking area identities (TAIs), Paging Priority, UE Radio Capabilityfor Paging, Assistance Data for Paging, Paging eDRX Information andExtended UE Identity Index Value.

The method may further comprise receiving a paging message generated bya radio resource control (RRC) layer of the CU.

The method may further comprise transmitting a paging record indicationbased on the paging information.

The paging record indication may include UE identity, paging frame (PF)and paging occasion (PO).

The method may further comprise receiving the paging message from the CUcorresponding the PO and the PF by a container.

The paging message includes a paging record list to page multiple UEs.

According to another embodiment of the present invention, a DistributedUnit (DU) of a base station in a wireless communication system includes:a memory; a transceiver for transmitting or receiving a radio signal;and a processor coupled to the transceiver, wherein the processorconfigured to: receive a paging information from a Central Unit (CU) ofthe base station; and transmit a paging message based on the paginginformation to a User Equipment (UE), wherein the DU is a lower layer ofthe base station, and the CU is a higher layer of the base station.

The CU includes a radio resource control (RRC) layer and a packet dataconvergence protocol (PDCP) layer of the base station, and wherein theDU includes a radio link control (RLC) layer, a medium access control(MAC) layer and a physical (PHY) layer of the base station.

The paging information may include at least one of UE Identity IndexValue, UE Paging Identity, Paging Discontinuous Reception (DRX), List oftracking area identities (TAIs), Paging Priority, UE Radio Capabilityfor Paging, Assistance Data for Paging, Paging eDRX Information andExtended UE Identity Index Value.

The processor may be further configured to receive a paging messagegenerated by a radio resource control (RRC) layer of the CU.

The processor may be further configured to transmit a paging recordindication based on the paging information.

The paging record indication may include UE identity, paging frame (PF)and paging occasion (PO).

The processor may be further configured to receive the paging messagefrom the CU corresponding the PO and the PF by a container.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of a control plane protocol stack of an LTEsystem.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem.

FIG. 4 shows a structure of a 5G system.

FIG. 5 shows the radio interface protocol for the user plane of the 5Gsystem.

FIG. 6 illustrates a Centralized Deployment scenario.

FIG. 7 shows a functional split between a central unit and a distributedunit in a separate base station deployment scenario.

FIG. 8 shows an example of a method for transmitting a paging messageaccording to an embodiment of the present invention.

FIG. 9 is a flowchart illustrating a method of transmitting a pagingmessage according to an embodiment of the present invention.

FIG. 10 is a flowchart illustrating a method of transmitting a pagingmessage according to another embodiment of the present invention.

FIG. 11 shows a communication system to implement an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN may include at least one evolved node-B (eNB) 20, and aplurality of UEs may be present in one cell. An E-UTRAN system is asystem evolved from the existing UTRAN system, and may be, for example,a 3GPP LTE/LTE-A system. The E-UTRAN consists of base stations (BSs) (oreNBs) which provide the UE with control plane and user plane protocols,and the BSs are connected through an X2 interface. An X2 user plane(X2-U) interface is defined between the BSs. The X2-U interface providesnon-guaranteed delivery of a user plane packet data unit (PDU). An X2control plane (X2-CP) interface is defined between two neighboring BSs.The X2-CP performs a function of context delivery between BSs, userplane tunnel control between a source BS and a target BS,handover-related message delivery, uplink load management, or the like.The BS is connected to the UE through a radio interface, and isconnected to an evolved packet core (EPC) through an S1 interface. An S1user plane (S1-U) interface is defined between the BS and a servinggateway (S-GW). An S1 control plane (S1-MME) interface is definedbetween the BS and a mobility management entity (MME). The S1 interfaceperforms an evolved packet system (EPS) bearer service managementfunction, a non-access stratum (NAS) signaling transport function,network sharing, an MME load balancing function, or the like. The S1interface supports a many-to-many relation between the BS and theMME/S-GW.

The eNB 20 provides the UE with end points of the control plane and theuser plane. The eNB 20 is generally a fixed station that communicateswith the UE 10 and may be referred to as another terminology, such as abase station (BS), a base transceiver system (BTS), an access point, orthe like. One eNB 20 may be arranged in every cell. At least one cellmay be present in a coverage of the eNB 20. One cell is configured tohave one of bandwidths selected from 1.25, 2.5, 5, 10, and 20 MHz, etc.,and provides downlink (DL) or uplink (UL) transmission services toseveral UEs. In this case, different cells may be configured to providedifferent bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in chargeof control plane functions, and a system architecture evolution (SAE)gateway (S-GW) which is in charge of user plane functions. The MME/S-GW30 may be positioned at the end of the network and connected to anexternal network. The MME has UE access information or UE capabilityinformation, and such information may be primarily used in UE mobilitymanagement. The S-GW is a gateway of which an endpoint is an E-UTRAN.The MME/S-GW 30 provides an end point of a session and mobilitymanagement function for the UE 10. The EPC may further include a packetdata network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which anendpoint is a PDN.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, Inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), P-GW and S-GW selection,MME selection for handovers with MME change, serving GPRS support node(SGSN) selection for handovers to 2G or 3G 3GPP access networks,roaming, authentication, bearer management functions including dedicatedbearer establishment, support for public warning system (PWS) (whichincludes earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission. The S-GW host providesassorted functions including per-user based packet filtering (by e.g.,deep packet inspection), lawful interception, UE Internet protocol (IP)address allocation, transport level packet marking in the DL, UL and DLservice level charging, gating and rate enforcement, DL rate enforcementbased on APN-AMBR. For clarity MME/S-GW 30 will be referred to hereinsimply as a “gateway,” but it is understood that this entity includesboth the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the eNB 20 are connected by means of a Uu interface. TheeNBs 20 are interconnected by means of an X2 interface. Neighboring eNBsmay have a meshed network structure that has the X2 interface. The eNBs20 are connected to the EPC by means of an S1 interface. The eNBs 20 areconnected to the MME by means of an S1-MME interface, and are connectedto the S-GW by means of S1-U interface. The S1 interface supports amany-to-many relation between the eNB 20 and the MME/S-GW.

The eNB 20 may perform functions of selection for gateway 30, routingtoward the gateway 30 during a radio resource control (RRC) activation,scheduling and transmitting of paging messages, scheduling andtransmitting of broadcast channel (BCH) information, dynamic allocationof resources to the UEs 10 in both UL and DL, configuration andprovisioning of eNB measurements, radio bearer control, radio admissioncontrol (RAC), and connection mobility control in LTE_ACTIVE state. Inthe EPC, and as noted above, gateway 30 may perform functions of pagingorigination, LTE_IDLE state management, ciphering of the user plane, SAEbearer control, and ciphering and integrity protection of NAS signaling.

FIG. 2 shows a block diagram of a control plane protocol stack of an LTEsystem, and FIG. 3 shows a block diagram of a user plane protocol stackof an LTE system.

Layers of a radio interface protocol between the UE and the E-UTRAN maybe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The radio interface protocol between the UE and the E-UTRAN maybe horizontally divided into a physical layer, a data link layer, and anetwork layer, and may be vertically divided into a control plane(C-plane) which is a protocol stack for control signal transmission anda user plane (U-plane) which is a protocol stack for data informationtransmission. The layers of the radio interface protocol exist in pairsat the UE and the E-UTRAN, and are in charge of data transmission of theUu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Data istransferred between the MAC layer and the PHY layer through thetransport channel. Between different PHY layers, i.e., a PHY layer of atransmitter and a PHY layer of a receiver, data is transferred throughthe physical channel using radio resources. The physical channel ismodulated using an orthogonal frequency division multiplexing (OFDM)scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physicaldownlink control channel (PDCCH) reports to a UE about resourceallocation of a paging channel (PCH) and a downlink shared channel(DL-SCH), and hybrid automatic repeat request (HARQ) information relatedto the DL-SCH. The PDCCH may carry a UL grant for reporting to the UEabout resource allocation of UL transmission. A physical control formatindicator channel (PCFICH) reports the number of OFDM symbols used forPDCCHs to the UE, and is transmitted in every subframe. A physicalhybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement(ACK)/non-acknowledgement (NACK) signal in response to UL transmission.A physical uplink control channel (PUCCH) carries UL control informationsuch as HARQ ACK/NACK for DL transmission, scheduling request, and CQI.A physical uplink shared channel (PUSCH) carries a UL-uplink sharedchannel (SCH).

A physical channel consists of a plurality of subframes in time domainand a plurality of subcarriers in frequency domain. One subframeconsists of a plurality of symbols in the time domain. One subframeconsists of a plurality of resource blocks (RBs). One RB consists of aplurality of symbols and a plurality of subcarriers. In addition, eachsubframe may use specific subcarriers of specific symbols of acorresponding subframe for a PDCCH. For example, a first symbol of thesubframe may be used for the PDCCH. The PDCCH carries dynamic allocatedresources, such as a physical resource block (PRB) and modulation andcoding scheme (MCS). A transmission time interval (TTI) which is a unittime for data transmission may be equal to a length of one subframe. Thelength of one subframe may be 1 ms.

The transport channel is classified into a common transport channel anda dedicated transport channel according to whether the channel is sharedor not. A DL transport channel for transmitting data from the network tothe UE includes a broadcast channel (BCH) for transmitting systeminformation, a paging channel (PCH) for transmitting a paging message, aDL-SCH for transmitting user traffic or control signals, etc. The DL-SCHsupports HARQ, dynamic link adaptation by varying the modulation, codingand transmit power, and both dynamic and semi-static resourceallocation. The DL-SCH also may enable broadcast in the entire cell andthe use of beamforming. The system information carries one or moresystem information blocks. All system information blocks may betransmitted with the same periodicity. Traffic or control signals of amultimedia broadcast/multicast service (MBMS) may be transmitted throughthe DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the networkincludes a random access channel (RACH) for transmitting an initialcontrol message, a UL-SCH for transmitting user traffic or controlsignals, etc. The UL-SCH supports HARQ and dynamic link adaptation byvarying the transmit power and potentially modulation and coding. TheUL-SCH also may enable the use of beamforming. The RACH is normally usedfor initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to aradio link control (RLC) layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides a function ofmapping multiple logical channels to multiple transport channels. TheMAC layer also provides a function of logical channel multiplexing bymapping multiple logical channels to a single transport channel. A MACsublayer provides data transfer services on logical channels.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer. The logicalchannels are located above the transport channel, and are mapped to thetransport channels.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting MBMS control information from the networkto a UE. The DCCH is a point-to-point bi-directional channel used by UEshaving an RRC connection that transmits dedicated control informationbetween a UE and the network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function ofadjusting a size of data, so as to be suitable for a lower layer totransmit the data, by concatenating and segmenting the data receivedfrom an upper layer in a radio section. In addition, to ensure a varietyof quality of service (QoS) required by a radio bearer (RB), the RLClayer provides three operation modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM). The AM RLCprovides a retransmission function through an automatic repeat request(ARQ) for reliable data transmission. Meanwhile, a function of the RLClayer may be implemented with a functional block inside the MAC layer.In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. ThePDCP layer provides a function of header compression function thatreduces unnecessary control information such that data being transmittedby employing IP packets, such as IPv4 or IPv6, can be efficientlytransmitted over a radio interface that has a relatively smallbandwidth. The header compression increases transmission efficiency inthe radio section by transmitting only necessary information in a headerof the data. In addition, the PDCP layer provides a function ofsecurity. The function of security includes ciphering which preventsinspection of third parties, and integrity protection which preventsdata manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer takes a role of controlling a radioresource between the UE and the network. For this, the UE and thenetwork exchange an RRC message through the RRC layer. The RRC layercontrols logical channels, transport channels, and physical channels inrelation to the configuration, reconfiguration, and release of RBs. AnRB is a logical path provided by the L1 and L2 for data delivery betweenthe UE and the network. That is, the RB signifies a service provided theL2 for data transmission between the UE and E-UTRAN. The configurationof the RB implies a process for specifying a radio protocol layer andchannel properties to provide a particular service and for determiningrespective detailed parameters and operations. The RB is classified intotwo types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB isused as a path for transmitting an RRC message in the control plane. TheDRB is used as a path for transmitting user data in the user plane.

A non-access stratum (NAS) layer above the RRC layer performs functions,such as session management and mobility management.

Hereinafter, a 5G network structure is described.

FIG. 4 shows a structure of a 5G system.

In case of an evolved packet core (EPC) having a core network structureof the existing evolved packet system (EPS), a function, a referencepoint, a protocol, or the like is defined for each entity such as amobility management entity (MME), a serving gateway (S-GW), a packetdata network gateway (P-GW), or the like.

On the other hand, in case of a 5G core network (or a NextGen corenetwork), a function, a reference point, a protocol, or the like isdefined for each network function (NF). That is, in the 5G core network,the function, the reference point, the protocol, or the like is notdefined for each entity.

Referring to FIG. 4, the 5G system structure includes at least one UE10, a next generation-radio access network (NG-RAN), and a nextgeneration core (NGC).

The NG-RAN may include at least one gNB 40, and a plurality of UEs maybe present in one cell. The gNB 40 provides the UE with end points ofthe control plane and the user plane. The gNB 40 is generally a fixedstation that communicates with the UE 10 and may be referred to asanother terminology, such as a base station (BS), a base transceiversystem (BTS), an access point, or the like. One gNB 40 may be arrangedin every cell. At least one cell may be present in a coverage of the gNB40.

The NGC may include an access and mobility function (AMF) and a sessionmanagement function (SMF) which are responsible for a function of acontrol plane. The AMF may be responsible for a mobility managementfunction, and the SMF may be responsible for a session managementfunction. The NGC may include a user plane function (UPF) which isresponsible for a function of a user plane.

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 and the gNB 40 may be connected by means of a Uu interface.The gNBs 40 may be interconnected by means of an X2 interface.Neighboring gNBs 40 may have a meshed network structure based on an Xninterface. The gNBs 40 may be connected to an NGC by means of an NGinterface. The gNBs 40 may be connected to an AMF by means of an NGCinterface, and may be connected to a UPF by means of an NG-U interface.The NG interface supports a many-to-many-relation between the gNB 40 andthe AMF/UPF 50.

A gNB host may perform functions such as functions for radio resourcemanagement, IP header compression and encryption of user data stream,selection of an AMF at UE attachment when no routing to an AMF can bedetermined from the information provided by the UE, routing of userplane data towards UPF(s), scheduling and transmission of pagingmessages (originated from the AMF), scheduling and transmission ofsystem broadcast information (originated from the AMF or O&M), ormeasurement and measurement reporting configuration for mobility andscheduling.

An access and mobility function (AMF) host may perform primary functionssuch as NAS signaling termination, NAS signaling security, AS securitycontrol, inter CN node signaling for mobility between 3GPP accessnetworks, idle mode UE reachability (including control and execution ofpaging retransmission), tracking area list management (for UE in idleand active mode), AMF selection for handovers with AMF change, accessauthentication, or access authorization including check of roamingrights.

A user plane function (UPF) host may perform primary functions such asanchor point for Intra-/inter-RAT mobility (when applicable), externalPDU session point of interconnect to data network, packet routing &forwarding, packet inspection and user plane part of policy ruleenforcement, traffic usage reporting, uplink classifier to supportrouting traffic flows to a data network, branching point to supportmulti-homed PDU session, QoS handling for user plane, e.g. packetfiltering, gating, UL/DL rate enforcement, uplink traffic verification(SDF to QoS flow mapping), transport level packet marking in the uplinkand downlink, or downlink packet buffering and downlink datanotification triggering.

A session management function (SMF) host may perform primary functionssuch as session management, UE IP address allocation and management,selection and control of UP function, configuring traffic steering atUPF to route traffic to proper destination, controlling part of policyenforcement and QoS, or downlink data notification.

Hereinafter, an RRC_INACTIVE state of a UE is described.

In the discussion on the NR standardization, an RRC_INACTIVE state (RRCinactive state) has been newly introduced in addition to the existingRRC_CONNETED state and RRC_IDLE state. The RRC_INACTIVE state may be aconcept similar to a lightly connected mode which is under discussion inLTE. The RRC_INACTIVE state is a state introduced to efficiently managea specific UE (for example, mMTC UE). A UE in the RRC_INACTIVE stateperforms a radio control procedure similarly to a UE in the RRC_IDLEstate in order to reduce power consumption. However, the UE in theRRC_INACTIVE state maintains a connection state between the UE and anetwork similarly to the RRC_CONNECTED state in order to minimize acontrol procedure required when transitioning to the RRC_CONNECTEDstate. In the RRC_INACTIVE state, a radio access resource is released,but wired access may be maintained. For example, in the RRC_INACTIVEstate, the radio access resource is released, but an NG2 interfacebetween a gNB and am NGC or an S1 interface between an eNB and an EPCmay be maintained. In the RRC_INACTIVE state, a core network recognizesthat the UE is normally connected to a BS. On the other hand, the BS maynot perform connection management for the UE in RRC_INACTIVE state.

FIG. 5 shows the radio interface protocol for the user plane of the 5Gsystem.

Referring to FIG. 5, the radio interface protocol of the 5G system withrespect to the user plane may include a new layer called Service DataAdaptation Protocol (SDAP) as compared with the LTE system. The mainservices and functions of the SDAP layer are the mapping between theQuality of Service (QoS) flow and the data radio bearer (DRB), and theQoS flow ID (QFI) marking in both DL and UL packets. The single protocolentity of the SDAP can be configured for each individual PDU session,except for the DC (dual connectivity) where two entities can beconfigured.

Hereinafter, a 5G RAN deployment scenario is described.

The 5G RAN can be classified into a non-centralized deployment scenario,a co-deployed deployment scenario (E-UTRA), and a co-located deploymentscenario according to the way in which the base station functions arearranged in a central unit and a distributed unit and a centralizeddeployment scenario and depending on coexistence with the 4G basestation. In this specification, 5G RAN, gNB, Next Generation Node B, NewRAN, and NR BS (New Radio Base Station) may mean a newly defined basestation for 5G.

FIG. 6 illustrates a Centralized Deployment scenario.

Referring to FIG. 6, the gNB may be divided into a central unit and adistributed unit. That is, the gNBs can be hierarchically separated andoperated. The central unit may perform the functions of the upper layersof the base station, and the distributed unit may perform the functionsof the lower layers of the base station.

FIG. 7 shows a functional split between a central unit and a distributedunit in a separate base station deployment scenario.

Referring to FIG. 7, in the case of Option 1, the RRC layer is in thecentral unit, and the PDCP layer, RLC layer, MAC layer, physical layer,and RF are in the distributed unit. In Option 2, the RRC layer and thePDCP layer are in the central unit, and the RLC layer, MAC layer,physical layer, and RF are in the distributed unit. In Option 3, the RRClayer, the PDCP layer and the RLC upper layer are in the central unit,and the RLC lower layer, MAC layer, physical layer, and RF are in thedistributed unit. In option 4, the RRC layer, the PDCP layer and the RLClayer are in the central unit, and the MAC layer, physical layer and RFare in the distributed unit. In option 5, the RRC layer, the PDCP layer,the RLC layer and the MAC upper layer are in the central unit, and theMAC lower layer, physical layer and RF are in the distributed unit. InOption 6, the RRC layer, PDCP layer, RLC layer and MAC layer are in thecentral unit, and the physical layer and RF are in the distributed unit.In Option 7, the RRC layer, the PDCP layer, the RLC layer, the MAClayer, and the upper physical layer are in the central unit, and thelower physical layer and RF are in the distributed unit. In option 8,the RRC layer, the PDCP layer, the RLC layer, the MAC layer, and thephysical layer are in the central unit and the RF is in the distributedunit.

Hereinafter, in this specification, the central unit may be referred toas a CU, and the distributed unit may be referred to as DU. The CU maybe a logical node that hosts the radio resource control (RRC), servicedata adaptation protocol (SDAP) and packet data convergence protocol(PDCP) layers of the gNB, DU may be a logical node that hosts a radiolink control (RLC), Media access control (MAC), and physical (PHY)layer. Alternatively, the CU may be a logical node hosting the RRC andPDCP layers of the en-gNB. That is, Option 2 in FIG. 7 described aboveis assumed in this specification.

Because the Paging message received from the Core Network (CN) can beinterpreted at the RRC layer in the CU but transmission of the paging ispossible in the DU through the radio, the signaling between the CU andthe DU is necessary. There is no procedure for performing the paging incase of CU-DU split. In other words, the CU can interpret the Pagingmessage received from the CN due to having the RRC layer, while itcannot page the UE directly due to not having the PHY layer. Thus, inorder to page the UE, the signaling between the CU and DU is necessary.However, there is no procedure for performing the paging in case ofCU-DU split. Therefore, the solution for this paging is needed.

Hereinafter, a method for transmitting a paging message according to anembodiment of the present invention is described.

FIG. 8 shows an example of a method for transmitting a paging messageaccording to an embodiment of the present invention.

In step S802, the DU receives a paging information from a Central Unit(CU) of the base station. The CU includes a radio resource control (RRC)layer and a packet data convergence protocol (PDCP) layer of the basestation, and wherein the DU includes a radio link control (RLC) layer, amedium access control (MAC) layer and a physical (PHY) layer of the basestation. The paging information includes at least one of UE IdentityIndex Value, UE Paging Identity, Paging Discontinuous Reception (DRX),List of tracking area identities (TAIs). Paging Priority, UE RadioCapability for Paging, Assistance Data for Paging, Paging eDRXInformation and Extended UE Identity Index Value. The DU receives apaging message generated by a radio resource control (RRC) layer of theCU. The DU may be further configured to transmit a paging recordindication based on the paging information. The paging record indicationincludes UE identity, paging frame (PF) and paging occasion (PO). The DUmay be further configured to receive the paging message from the CUcorresponding the PO and the PF by a container. The paging messageincludes a paging record list to page multiple UEs.

In step S804, the DU transmits the paging message based on the paginginformation to a User Equipment (UE).

FIG. 9 is a flowchart illustrating a method of transmitting a pagingmessage according to an embodiment of the present invention.

Referring to FIG. 9, according to an embodiment of present invention,the CU transmits the paging message generated by the RRC layer and theinformation included into the paging message received from the AMF as itis to the DU which should perform the paging, and then the DU determineshow to perform the paging.

In Step S902, the UE is in RRC_IDLE state.

In Step S904, the AMF sends the paging message to the CU.

In Step S906, on receiving the paging message, based on the informationincluded into the message, the CU determines which DU performs thepaging. And then, it sends the paging transfer or new message includingthe paging information to the DU which should perform the paging. Thepaging information may include the followings:

-   -   UE Identity Index Value    -   UE Paging Identity    -   Paging DRX    -   List of TAIs    -   Paging Priority    -   UE Radio Capability for Paging    -   Assistance Data for Paging    -   Paging eDRX Information    -   Extended UE Identity Index Value

Also, the paging transfer or new message may include the paging messagegenerated by the RRC layer. Further, paging DRX may be included in thepaging message, and the DU may use the paging DRX to determine the finalpaging cycle for the UE. Further, the paging priority may be included inthe paging message, and the DU may use the paging priority to page oneor more UEs. That is, the DU may determine several conditions for pagingUE, such as paging cycle, based on the paging information. In order toforward this paging message to the DU, a container may be used.

In Step S908, upon receipt of the paging transfer or new message, basedon the paging information, the DU decides when the paging is broadcastedor how frequently the paging is repeated or which level of power isnecessary to transmit the paging.

In Step S910, if the paging frame (PF) and paging occasion (PO) whichthe DU calculates for the UE are the same ones of other UE(s), the DUmay transmit to the CU the paging record indication or new messageincluding the UE identity (e.g., S-TMSI or IMSI), the PF, and the PO tobe able to page multiple UEs. Also, in this case, the DU may ignore thepaging message received from the CU in Step S906.

On the other hand, one paging occasion (PO) is a subframe where theremay be P-RNTI transmitted on PDCCH or MPDCCH or, for NB-IoT on NPDCCHaddressing the paging message. In P-RNTI transmitted on MPDCCH case, POrefers to the starting subframe of MPDCCH repetitions. In case of P-RNTItransmitted on NPDCCH, PO refers to the starting subframe of NPDCCHrepetitions unless subframe determined by PO is not a valid NB-IoTdownlink subframe then the first valid NB-IoT downlink subframe after POis the starting subframe of the NPDCCH repetitions.

One paging frame (PF) is one Radio Frame, which may contain one ormultiple Paging Occasion(s). When DRX is used the UE needs only tomonitor one PO per DRX cycle. PF, PO, and PNB are determined byfollowing formulae using the DRX parameters provided in SystemInformation:

PF is given by following equation:SFN mod T=(T div N)*(UE_ID mod N)

In Step S912, on receiving the message from the DU, the CU may generatethe paging message including the paging record list to page multiple UEswhich have the same PF and PO. That is, the received UE identity (e.g.,S-TMSI or IMSI) is contained into the paging record list correspondingto the received PF and PO. If there is no paging record listcorresponding to the received PF and PO, the CU may create the pagingrecord list.

In Step S914, The CU sends to the DU the paging transfer or new messageincluding the PF, the PO and the paging message. This paging message maycontain the paging record list corresponding to the transmitted PF andPO and may be piggybacked by a container.

On the other hand, Steps S910˜S914 may be skipped according onembodiments.

In Step S916, The DU pages the UE indicated in the paging record list.

In Step S918, on receiving the paging message, the UE initiates the UEtriggered Service Request procedure.

With this embodiment of present invention, the DU which should performthe paging can manage the paging and page the UE considering the radiocondition and/or radio resources.

FIG. 10 is a flowchart illustrating a method of transmitting a pagingmessage according to another embodiment of the present invention.

Referring to FIG. 10, according to an embodiment of present invention,after the CU determines how to perform the paging and the informationneeded to perform the paging, it sends this information and the UE ID orthe paging message generated by the RRC layer to the DU which shouldperform the paging.

In Step S1002, the UE is in RRC_IDLE state.

In Step S1004, The AMF sends the paging message to the CU.

In Step S1006, on receiving the paging message, based on the informationincluded into the message, the CU determines when the paging isbroadcasted or how frequently the paging is repeated or which level ofpower is necessary to transmit the paging or which DU performs thepaging.

In Step S1008, the CU transmits to the DU the Paging Transfer or newmessage including the UE ID or the paging message generated by the RRClayer, and the paging transmission information. The paging transmissioninformation may contain the followings:

-   -   Paging Frame (PF)    -   Paging Occasion (PO)    -   Paging Time Window (PTW)    -   Paging repetition/attempt number    -   Paging transmission power level    -   System Frame Number (SFN)

The paging message may be piggybacked by a container to the DU.

In Step S1010, upon receipt of the message from the CU, the DU pages theUE based on the paging transmission information.

In Step S1012, on receiving the paging message, the UE initiates the UEtriggered Service Request procedure.

With this another embodiment of present invention, the CU can manage thepaging received from the AMF and provide the DU which should perform thepaging with the information needed to perform the paging. Thisembodiment of the present invention can reduce the number of informationelements offered by the signaling between the CU and the DU.

In this invention, the CU or the DU can manage the paging. In case theCU manages the paging, it can provide to the DU with the informationneeded to perform the paging. In case the DU manage the paging, it canpage the UE considering the radio condition and/or radio resources.

FIG. 11 shows a communication system to implement an embodiment of thepresent invention.

A first network node 1100 includes a processor 1101, a memory 1102, anda transceiver 1103. The memory 1102 is coupled to the processor 1101,and stores a variety of information for driving the processor 1101. Thetransceiver 1103 is coupled to the processor 1101, and transmits and/orreceives a radio signal. The processor 1101 implements the proposedfunctions, procedures, and/or methods. In the aforementionedembodiments, an operation of the first network node may be implementedby the processor 1101.

A second network node 1110 includes a processor 1111, a memory 1112, anda transceiver 1113. The memory 1112 is coupled to the processor 1111,and stores a variety of information for driving the processor 1111. Thetransceiver 1113 is coupled to the processor 1111, and transmits and/orreceives a radio signal. The processor 1111 implements the proposedfunctions, procedures, and/or methods. In the aforementionedembodiments, an operation of the second network node 1110 may beimplemented by the processor 1111.

The processors 1111 may include application-specific integrated circuit(ASIC), other chipset, logic circuit and/or data processing device. Thememories may include read-only memory (ROM), random access memory (RAM),flash memory, memory card, storage medium and/or other storage device.The transceivers may include baseband circuitry to process radiofrequency signals. When the embodiments are implemented in software, thetechniques described herein can be implemented with modules (e.g.,procedures, functions, and so on) that perform the functions describedherein. The modules can be stored in memories and executed byprocessors. The memories can be implemented within the processors orexternal to the processors in which case those can be communicativelycoupled to the processors via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

What has been described above includes examples of the various aspects.It is, of course, not possible to describe every conceivable combinationof components or methodologies for purposes of describing the variousaspects, but one of ordinary skill in the art may recognize that manyfurther combinations and permutations are possible. Accordingly, thesubject specification is intended to embrace all such alternations,modifications and variations that fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for a wireless device in a wirelesscommunication system, the method comprising: receiving a paging from adistribution unit (DU) of a base station; and upon receiving the paging,initiating a service request procedure, wherein the paging is based onpaging information transmitted from a central unit (CU) of the basestation to the DU of the base station, wherein the paging informationincludes paging discontinuous reception (DRX) information and pagingpriority information, wherein the DU of the base station has a radiolink control (RLC) layer, a media access control (MAC) layer and aphysical layer of the base station, and wherein the CU of the basestation has a radio resource control (RRC) layer, a service dataadaptation protocol (SDAP) layer, and a packet data convergence protocol(PDCP) layer of the base station.
 2. The method of claim 1, wherein acycle of the paging is determined based on the paging DRX information.3. The method of claim 1, wherein the paging information furtherincludes at least one of a user equipment (UE) identity index value, aUE paging identity, a list of tracking area identities (TAIs), UE radiocapability for paging, assistance data for paging and/or an extended UEidentity index value.
 4. A wireless device in a wireless communicationsystem, the wireless device comprising: at least one transceiver; atleast processor; and at least one computer memory operably connectableto the at least one processor and storing instructions that, based onbeing executed by the at least one processor, perform operationscomprising: receiving a paging from a distribution unit (DU) of a basestation; and upon receiving the paging, initiating a service requestprocedure, wherein the paging is based on paging information transmittedfrom a central unit (CU) of the base station to the DU of the basestation, wherein the paging information includes paging discontinuousreception (DRX) information and paging priority information, wherein theDU of the base station has a radio link control (RLC) layer, a mediaaccess control (MAC) layer and a physical layer of the base station, andwherein the CU of the base station has a radio resource control (RRC)layer, a service data adaptation protocol (SDAP) layer, and a packetdata convergence protocol (PDCP) layer of the base station.
 5. Thewireless device of claim 4, wherein a cycle of the paging is determinedbased on the paging DRX information.
 6. The wireless device of claim 4,wherein the paging information further includes at least one of a userequipment (UE) identity index value, a UE paging identity, a list oftracking area identities (TAIs), UE radio capability for paging,assistance data for paging and/or an extended UE identity index value.7. A wireless device in a wireless communication system, the wirelessdevice comprising: a processor; and a memory coupled to the processor,wherein the processor is configured to: obtain a paging from adistribution unit (DU) of a base station; and upon obtaining the paging,initiate a service request procedure, wherein the paging is based onpaging information transmitted from a central unit (CU) of the basestation to the DU of the base station, wherein the paging informationincludes paging discontinuous reception (DRX) information and pagingpriority information, wherein the DU of the base station has a radiolink control (RLC) layer, a media access control (MAC) layer and aphysical layer of the base station, and wherein the CU of the basestation has a radio resource control (RRC) layer, a service dataadaptation protocol (SDAP) layer, and a packet data convergence protocol(PDCP) layer of the base station.
 8. The wireless device of claim 7,wherein a cycle of the paging is determined based on the paging DRXinformation.
 9. The wireless device of claim 7, wherein the paginginformation further includes at least one of a user equipment (UE)identity index value, a UE paging identity, a list of tracking areaidentities (TAIs), UE radio capability for paging, assistance data forpaging and/or an extended UE identity index value.